Electric tracer for profiling machine tools



June 14, 1966 F. LASERMANN ELECTRIC TRACER FOR PROFILING MACHINE TOOLSFiled Feb. 5, 1965 5 Sheets-Sheet 1 lnvenfar: FfLasermcmn A-r-rokNEasJune 14, 1966 F. LASERMANN 3,255,670

ELECTRIC TRACER FOR PROFILING MACHINE TOOLS Filed Feb. 5, 1965 5Sheets-Sheet 2 Fig. 2

Fig. 4

Inventor.- ELczser/mlnn f org/W ATTORNEHS June 14, 1966 F. LASERMANNELECTRIC TRACER FOR PROFILING MACHINE TOOLS 5 Sheets-Sheet 5 Filed Feb.5, 1965 Fig. 3

lnvenior: F. Lasermcm United States Patent O 9 Claims. or. 90-62) Thepresent invention relates to profiling machine tools and particularly toan electrical tracer for machines of this type. Tracers of this type aresuitable for all types of profiling work, particularly for planetarymilling, rapid return milling and profile milling. I

An object of the invention is to improve the precision of a profilingprocedure, so that the errors produced by the tracer during the sensingof a shape, are reduced or completely compensated.

According to the present invntion, an electric tracer for profilingmachine tools comprises a tracer point held in a ball'and socket jointand issuing above said joint into a casing, said casing acting on aswash plate for forward movement, four mutually opposite sensing membersar-.

ranged on said swash plate symmetrically to the axis of said casing,said members producing one set of electric signals proportional to thedeflection of the tracer point and a core rod disposed along the axis ofsaid casing, an extension of said core rod acting upon sensing means toproduce another set of electric signals proportional to its deflection,said other set being superimposed on said one set of signals so as toreduce deflection errors of the tracer point. The sensing membersarranged on the swash plate may be constructed asiron-cored magnets,which are rotatable with the swash plate opposite its armature coil discattached to the core rod. The ironcored magnets are suitably locatedwith their pole surfaces in a plane parallel to the axis of the tracercasing and the pole surfaces of the iron-cored magnets are suitablylocated on the surface of a cylindrical jacket, which surrounds therarmature coil discs.

According to another embodiment of the invention, the sensing membersarranged on the swach plate consist of quadrants, over which armaturecoils are arranged on a disc rotatable about the core rod. This disc isrotated by an adjusting motor, secured to the core rod and controlled.by the corrector signals of the sensing members on the core rod, in thesense of a reduction of the deflection error relative to the armaturediscs. The sensing means on .the core rod preferably consists of anarmature disc, which is reciprocably movable between two fixed armaturecoils in the direction of its axis, during the deflecting movements ofthe core rod. A mechanical barrier is arranged .on the tracer casing,which barrier while in operation connects casing and core rod, so thatthe forward movements of the swash plate are prevented.

The invention may be understood more fully from the followingdescription of specific embodiments with referece to the accompanyingdrawings wherein:

FIGURE 1 is a vertical section through a tracer according to theinvention;

FIGURE 2 is a section along the line 11-11 of FIG- URE 1;

FIGURE 3 is a vertical section through another embodiment of a traceraccording to the invention;

FIGURE 4 is a section along the line IV-IV of FIGURE 3.

The profiling tracer according to the invention comprises in knownmanner a tracer point 1, which is fixed in a ball-and-socket joint 2,and issues above the balland-socket joint into :a tracer casing 3. Acore rod 4 is arranged within said casing 3, which rod is supportedwithball sockets and balls 5 on its lower end in the centre of theball-and-socket joint 2. The casing 3 ends somewhat in the middle of thecore rod 4 and is connected during the deflection movements of thetracer point 1 to its annular head 6 arranged on the upper end, onlyafter :a certain forward movement has been covered, against a flange 7on the core rod. Inthis way, a very delicate, doubled lever transmissionis achieved in a very limited space in addition to the forward movement.

The annular head 6 on the upper end of the tracer casing 3 is locatedoutwardly free from play against a casing projection 8 of a swash plate9 The swash plate 9 is pivotally arranged on the core rod 4 by means ofthe ball-and-socket joint 14 and is held in 'its central position bymeans of a disc washer 11, which is securely connected to the core rod4, and by means of a cap disc 10 supported by springs 13.

Approximately quadrant-shaped armature discs 16 and 17 are arranged nearthe periphery of the swash plate 9. These four armature discs arelocated symmetrically to the axis of the tracer. A disc 18 is rotatablyfixed to the core rod 4 above the swash plate, on which disc mag neticcoils 19 and 20 are arranged in such a way that they lie opposite oneanother, and are also symmetrical to the axis of the tracer and one ofthe magnetic. coils being always assigned to an armature disc 16 or 17.Said armature discs and magneic coils form the sensing members whichproduce sigals when the tracer point 1 is deflected. Two oppositesensing members always form a half-bridge, the second half-"bridge beinglocated in the control part and the variable distance of the armaturedisc 16 or 17 from the armature coil 19 or 20, producing signalvoltages, which correspond in size and polarity to the direction of thetangent of the scanned model contour. Said signal voltages are conveyedto the amplifier and are used for controlling the servo-motors in the Xand Y coordinates.

The upper end of core rod 4 is also held by a ball 21 secured in ballsockets. The upper support 22 of the core rod issues into a rod 23,which is guided in a fixed bearing 24, so that it may effect only axialmovements. A spring 25 is arranged above the rod 23, which spring isalso supported against a fixed bearing 26 and presses the bar 23 in lineon the bearing of the core rod. An armature disc 27 is secured to therod 23, which disc is reciprocably movable between two secured armaturecoils 28 and 29. This armature disc 27 forms with both magnetic coils 28and 29 another sensing means, the signals of which on the one handsuperpose the signals of the sensing members on the swash plate 9 and onthe other hand serve to control a motor 30, which is arranged 'near theupper end of the core rod 4 and with a reduction gear 31, the rotatabledisc-18 with the armature coils 19 and 20 located thereon, may rotateabout a quarter turn according to the signals received by thesensingmembers 27 and 29.

On the casing 3 is arranged a disc casing 32, by means of its balls 33or even locking wedges which are set in the casing wall, maybe pressedagainst the core rod 4. This casing 32, together with the balls 73,forms a mechanical lock, it it is shifted upwards corresponding to thediagrammatical drawing, and connects casing and core rod securelytogether, so that forward movements of the swash plate 9 are stopped.Such a locking of the forward movements is desired, for planetarymilling or rapid return milling. I

A tracer according to FIGURES ,3 and 4 is essentially constructed in avery similar way to the previously described tracer. The same referencenumerals are used for the same parts. The construction of the lower partof the tracer with casing 3 and core rod 4 corresponds to that of theabove-described example. of the casing 3, a casing 35 is rotatablyarranged on ball bearings 34, which casing issues upwardly into a plate36, which is located at the approximate height of the upper end of thecasing, and on which iron-cored magnets 37, 38, 39 and 40 are arrangedin such :a way that, in pairs and opposite one another, they subdividethe circular disc 36 into quarter sections. The arrangement of theiron-cored magnets 37 to 40 may be particularly seen from FIGURE 4,which shows a section through this part of the tracer. The pole surfaces37a, 38a, 39a and 40a of said iron-cored magnets 37 to 40 are arrangedin such a way that they are located on a cylindrical jacket surface.This cylindrical jacket surface surrounds a disc 41 with armature discs42, 43, 44 and 45, which are located opposite the polar surfaces of theiron-cored magnets, always however surrounding about a quarter sectionof the circular disc 41. Between the armature discs 42 to 45 and thepole surfaces 37a to 40a, there is an air gap. The disc 41, on which thearmature discs 42 to 45 are arranged, is firmly fixed on the upper endof the core rod 4.

The rotatably arranged casing 35, with the plate 36 carrying theiron-cored magnets 37 to 40, is rotatable by means of a small motor 30through a driving pinion 31 and a belt 46 and may be rotated by mean-sof the motor 30 in the same way as the rotatable disc 18 with themagnets 19 and 20 fixed thereon according to the previously describedembodiment.

The sensing means 27 to 29 arranged above the core rod 4 is constructedin this embodiment in the same way as in the previously describedembodiment.

The function of the first tracer described-above is explained moreclearly later. The function of the second tracer described above issimilar in every respect:

The tracer point 1 is guided to the template in the directionpre-selected by hand (starting thrust). When the tracer point 1 is incon-tact with the template, the tracer casing 3, which is securely fixedto the tracer point, is swung over the ball-and-socket joint 2. At thesame time, by means of the free-from-play addition of the annular bead 6located at the upper end of the tracer casing 3 against the casingprojection 8, a shifting of the swash plate 9 from the central positionis produced, namely about an axis parallel to the tangent of the curvedform in the mechanism point of the tracer point. Let it be assumed thatthe tracer point 1 is swung outwardly to the left, then the swash plate9 tilts about an axis, which stands vertical on the plane of the drawingin the centre of the balland-socket'joint 14, and the right armaturedisc 16 approaches the opposite armature coil 19 from its normalposition, the left armature disc 18 is removed from the oppositearmature coil 19, and said coordinate-data sensing members the delivercorresponding signal voltages.

If the tracer point 1 is deflected further, the annular head 6 islocated on the upper end of the feeler casing 3 against the flange 7 ofthe core rod 4 and deflects the core rod. This deflection causes theball to leave its balland-socket joint so that the bearing distance ofthe core rod becomes greater. The outer support 22 is put under pressureagainst the effect of the springZS, and the bearing rod 23 shifts thearmature plate 27 secured thereto in line on the upper armature coil 29.The arrangement is such that the armature disc 27 is located veryclosely above the lower armature coil 28 when the system is in normalposition. If, through a deflection of the tracer point 1 the armaturedisc 27 comes after starting into the central position on the contour ofthe template the starting thrust is released, and the profiling processis started. The signal of the sensing means 27 to 29 produced when thecentre position of the armature disc 7.7 is reached, thus shows the wayto the servo-motors for On the upper end the X and Y coordinates even tothe signals produced by the sensing members 19, 20 on the swash plate.

As soon as the profiling process has started, an almost tangentialmovement, opposite the direction of movement, of the signal voltages ofthe sensing members is produced on the swash plate by the friction ofthe tracer point on the template. Consequently, the tracer point isdeflected more or less after each inclination of the con tour on thetemplate. When the tracer is deflected the armature disc 27 also movesfrom its centre position and in an upward movement gives a negativesignal rising from nil or in a downward movement a positive signalrising from nil. The signals of the sensing means 27 to 29 aresuperposed on the signals of the sensing members 16, 19 and 17, 20 inthe radial forward deflection, so that they are effective in the senseof a reduction of the deviation; i.e., if the tracer 1 is furtherdeflected and the sensing means 27 to 29 releases a rising negativesignal, this value is subtracted from the signal of the direction ofmovement, which may be seen from the reference, and is added to thesignal of the direction displaced for this purpose about When thedeflection of the tracer point 1 is reduced below the centre position ofthe axial sensing means 27 to 29, the superimposition results in theopposite sense, it is thus the rising positive signal which is added tothe signal of the direction of movement, which is shown in thereference, and subtracted from the signal of the direction displaced forthis purpose about 90.

The production of the corrector signal by the sensing means 27. to 29requires an alteration of the deflection of the tracer and thereforealso a deviation of the theoretical contour of the template. Since thevalue on a 360 circuit is not constant according to experience, that isit is conditioned by variable friction values between tracer point andtemplate as well as frictions in the mechanical part of the tracer aswell as on deviations from proportionality of the tracer deflection tothe released signal, this tracking error may be compensated by a tracerpoint offset by a small value. In order to reduce the tracking errorstill further, the corrector signal produced by the sensing means 27 to29 is still given to the servomotor 30, which shifts the holding disc 18with the armature coils 19 and 20 in line to a zero tracking error.

By means of the cited error effects, the tangent of the movement of thetracer point is inclined opposite the tangent of the template in theactual operating position of the tracer point during the profilingprocess. Both tangents do not correspond The difference of inclinationbetween the actual tangent (of the movement) and the theoretical tangent(of the template) is determined by the sensing means 27 to 29, the errorsignal of which becomes elfective for correction at two differentpositions namely once in elfect on the servo motor 30, the error isprevented from exceeding a certain magnitude and in the effect on thesensing members 16, 17 and 19, 29 arranged in the quadrants, acorresponding error is further minimised.

It will be understood that the above-described embodiments are intendedto be only by way of illustrative example and that modifications may bemade in various ways apparent to those skilled in the art withoutdeparting from the scope of the invention, and that this is limited onlyby the appended claims.

I claim:

1. An electric tracer for profiling machine tools comprising a tracerpoint held in a ball and socket joint and issuing above said joint intoa casing, said casing acting on a swash plate for forward movement, fourmutually opposite sensing members arranged on said swash platesymmetrically to the axis of said casing, said members producing one setof electric signals proportional to the deflection of the tracer pointand a core rod disposed along the axis of said casing, an extension ofsaid core rod acting upon sensing means to produce another set ofelectric signals proportional to its deflection, said other set beingsuperimposed on said set of signals so as to reduce deflection errors ofthe tracer point.

2. An electric tracer according to claim 1, wherein said sensing membersare constructed as iron-cored magnets which, with the swash plate, arerotatable opposite corresponding armature discs secured on a disc tosaid core rod. 1

3. An electric tracer according to claim 2, wherein said iron-coredmagnets are arranged with their pole surfaces in a plane parallel to theaxis of said tracer casing.

4. An electric tracer according to claim 3, wherein the pole surfaces ofthe iron-cored magnets are located on the surface of a cylindricaljacket, which surrounds the said disc and said armature discs.

5. An electric tracer according to claim 1, wherein said sensing memberscomprise approximately quartersectioned armature discs above whicharmature coils are arranged on a disc rotatably fixed to said core rod.

6. An electric tracer according to claim 5, wherein said disc isrotatable by a servo motor securely fixed to said core rod andcontrolled by corrector signals from said sensing means, said signalsbeing in the sense of an extension of the deflection error opposite thedeflection disc.

7. An electric tracer according to claim 5, wherein said disc isrotatable by a servo motor securely fixed to said casing and controlledby corrector signals from said sensing means said signals being in thesense of an extension of the deflection error opposite the deflectionoperation, whereby 'the forward movement of the swash plate is locked.

No references cited.

WILLIAM W. DYER, JR, Primary Examiner.

G. A. DOST, Assistant Examiner.

1. AN ELECTRIC TRACER FOR PROFILING MACHINE TOOLS COMPRISING A TRACERPOINT HELD IN A BALL AND SOCKET JOINT AND ISSUING ABOVE SAID JOINT INTOA CASING, SAID CASING ACTING ON A SWASH PLATE FOR FORWARD MOVEMENT, FOURMUTUALLY OPPOSITE SENSING MEMBERS ARRANGED ON SAID SWASH PLATESYMMETRICALLY TO THE AXIS OF SAID CASING, SAID MEMBERS PRODUCING ONE SETOF ELECTRIC SIGNALS PROPORTIONAL TO THE DEFLECTION OF THE TRACER POINTAND A CORE ROD DISPOSED ALONG THE AXIS OF SAID CASING, AN EXTENSION OFSAID CORE ROD ACTING UPON SENSING MEANS TO PRODUCE ANOTHER SET OFELECTRIC SIGNALS PROPORTIONAL TO ITS DEFLECTION, SAID OTHER SET BEINGSUPERIMPOSED ON SAID SET OF SIGNALS SO AS TO REDUCE DEFLECTION ERRORS OFTHE TRACER POINT.